Build a 3DoF gear pantograph
A pantograph is a mechanical system that allows a human being to reproduce a drawing he makes at a higher or smaller scale. The main property is to send a force from one end to another end. The classical pantograph has 2DoF, thus it allows drawing in 2D on both horizontal and vertical axis.
The property of transferring forces came to my attention and I found it interesting to be applied for teaching and training other persons complicated stuff such as (writing for young children, playing guitar for all-age people).
However, human hands are used to do 3DoF movements, thus this is one need to implement for my objective.
Moreover, the classical pantograph is a passive system. This means that for my idea another person should be the one who teaches the person who receives the force. But we can do better in the actual world, we can add actuators to the first end of the pantograph and make them send different forces for different tasks.
What did I need for my project?
Wood 3mm thickness for cutting gears, servomotors as actuators
1. Create the gears
- at first, I wanted to 3D print the gears, but Romain recommended me to use the laser cutter – this was a more efficient and faster method
- to generate the gears I used a website called: www.geargenerator.com
- this website made it easy to create gears of different sizes and with different number of teeths.
- I created 2 gears of same size with number of teeth = 20 and 1 smaller gear with number of teeth = 13. The size of teeths were equal for these 3 gears in order to insure a good motion.
- this website made it easy to export each gear to a .SVG file that I further edited in InkScape.
2. Create a 2DoF pantograph
- used the 3 gears from step 1
- set-up the laser-cutter only for cutting (instructions followed are from my prev documentation which you can find here: https://fablabdigiscope.wordpress.com/2015/12/10/documentation-week-2-learning-how-to-use-the-laser-cutter-razvan-ursachi/
- after cutting them, in order to make them move together, I had to connect them to the same ground
- I did some iterations here and the most stable version involved cutting a « + » to the middle of the gear.
- an additional piece went through this « + » and through the ground as well as you can see in the picture below
- however, in the ground piece I cut a circle and not a + in order to allow the movement of the gears
- there are 2 ground pieces: one coming above the gears and another one below the gears
Just having the gears and the connectors allowed me to create just a 1DoF mechanical system (only for horizontal movements). However, the force send was equal. The objective from now on was to create the other 2 dimensions for the mechanical system.
3. Design the 3DoF mechanical system
- to do this, I used Autodesk Maya for designing in detail a 3D visual description of what I will have to laser cut during the next steps.
- firstly, I created the system I have already implemented.
- secondly, I decided that the best way to go is to add two tracks to the sides that will make possible moving the gears back and forth, thus allowing the 2nd DoF, the vertical dimension.
- designing the 3rd DoF, the z dimension sending of force made it all harder. I decided to make use of the panels that are moving on the tracks and to design an additional piece with connectors as did before.
- I also considered to enforce this mechanism by adding 2 milestones that should insure that the force is passing at the same value.
- the final result included all the 3DoF now, but it was only designed.
4. Laser cutting the pieces
- having the design was really helpful because it made easier to create the pieces directly in CorelDraw.
- all I had to do was to create simple rectangles and copy the design of the connectors created before.
- I also laser cut a second set of gears.
This first result is not very stable and implements only 2DoF remaining to laser cut the tracks. However, sending the forces from one side to the other works greatly. Right now, a human being handling the first end can send a horizontal x force combined with a spatial z force to the one handling the second end.
5. Future work
One of my main objectives was to make this an active mechanism, but it was not possible until now, thus in future work I would like to add this by designing a system with servomotors driven by Arduino. This system will be in charge of moving one handle.